Generally, golf balls have been classified as solid balls or wound balls. Solid balls are typically comprised of a solid, polymeric core and a cover. These balls are generally easy to manufacture, but are regarded as having non-optimal or limited playing characteristics. Wound balls are comprised of a solid or liquid-filled center surrounded by tensioned elastomeric material and a cover. Wound balls generally have good playing characteristics, but are more difficult to manufacture than solid balls.
The prior art is comprised of various golf balls that have been designed to provide optimal playing characteristics. These characteristics include the initial velocity and spin of the golf ball, which can be optimized for various calibers of players. For instance, certain players prefer to play a ball that is softer feeling and has a high spin rate that allows the player to control or “work” the ball. However, balls of this nature tend to exhibit a slight decrease in distance due to the high spin rate. Other players prefer to play a ball that has a low spin rate to maximize distance. These balls, however, tend to be hard feeling and difficult to control around the greens.
Methods for producing golf balls having an ideal combination of the above mentioned desirable characteristics have been many. Manufacturers have molded layers around a solid center by placing a preformed center between two blocks of core material in a spherical compression mold, and closing the mold. This process, however, provides little control over the ultimate placement of the center within the golf ball core. Large variations in the location of the center can result and are extremely detrimental to ultimate golf ball performance. Another method that improves the centering of a solid center involves forming two hemispherical polymer cups with two mold halves that, when placed together, create a hollow cavity in which the solid center rests. The two cups are then heated above the curing temperature of the polymeric material, under compression, to form the golf ball core. However, although centering is improved, at certain desirable temperatures (typically higher) and material compositions (low levels of reinforcing polymer), the cups tend to pull away from the surface of the molds, which can result in a slightly off-center solid center because of displaced shell material.
When using methods that mold two cups together using heat, several concerns may occur. It is typically desirable to have a golf ball with uniform properties so that the ball may not respond differently when struck in one position versus another. In addition to achieving proper placement of a center, these concerns typically also involve the construction and dimple pattern on the outer cover of the ball.
A lack of uniformity in the construction or properties of other portions of the ball also may adversely affect ball performance. For example, when two cups are heated and molded together, the area of the ball around the parting line of the mold plates may have different properties than the rest of the molded ball component. The durability, elasticity, hardness, and the like, may be significantly different from other portions of the molded component. In addition, the molded component may have flash, or excess molding material, on the portion of the component corresponding to the parting line of the mold plates. Because prior molding processes only allow a small space for flash material to form, the application of heat and pressure that is involved in the molding process on the thin layer of flash material can cause it to cure at a much faster rate and to a much greater degree than the material that forms most of the molded component. This “super cured” region may extend into portions of the ball near the parting line of the mold, thereby allowing a portion of the ball to have different properties than other portions.
In addition to possibly causing the molded component to have non-uniform properties, the application of heat and pressure to this thin layer of flash can also make the removal of this material more difficult and/or time consuming. Usually, any excess material remaining on the molded ball component must be removed after the component has been removed from the mold. If the flash material is “super cured” as described above, it may be harder, and therefore more difficult to remove, than material having properties and a cure state more similar to the molded component. Because it is preferred that the molded component remain substantially spherical, the removal of this excess material can be costly and time consuming. Additionally, the by-product of processes involved in removing flash material while maintaining the molded component's substantially spherical shape usually is a sludge-like material of fine particulate material that can be difficult to reprocess.
In addition, prior art processes for forming a multi-layer core typically involved individually loading each cavity of a mold plate with material for forming the component. For instance, forming the outer shell of a dual core previously involved individually loading raw material into each cavity of a mold plate. Moreover, conventional process for loading raw material also usually require that the material be loaded with a particular orientation in order to better assure that the material would completely fill the cavity without leaving voids or trapped pockets of air during molding. The loading and orienting of the raw material into each cavity of a mold is a time consuming process.
Yet another disadvantage of current molding processes is that once the component is formed, it can be difficult to remove some of the molded components from the opened mold. The matrix of golf ball components that are molded at the same time often may not be sufficiently strong to assist in pulling a stuck component out of a cavity. Thus, attempts to remove stuck components by pulling on the flash material may only result in the flash material prematurely tearing away from the component while it is still in the mold. Removal of trapped components under conditions such as these can increase maintenance costs and reduce manufacturing efficiently by keeping the molding equipment out of service until the trapped component can be removed.
Therefore, what is desired is an improved and more efficient method of molding multi-layer cores that employs a center plate for compression molding.